Field of the Invention
The present invention relates to an endoscope apparatus and an image pickup control method thereof, and more particularly to an endoscope apparatus having a CMOS type solid-state image pickup element in a distal end portion of an endoscope, and an image pickup control method of the endoscope apparatus.
Description of the Related Art
Medical diagnosis utilizing an endoscope system is actively performed in the medical field. An endoscope system includes: an electronic endoscope that has an insertion portion that is inserted into a body cavity; a processor apparatus to which the electronic endoscope is detachably connected, and which receives an image pickup signal that is outputted from a solid-state image pickup element built into the electronic endoscope and performs image processing thereon, and outputs an observation image to a monitor; and a light source apparatus that generates light that passes through a light guide inside the electronic endoscope and illuminates the inside of the body cavity.
Although conventionally CCD (a charge coupled device) type image pickup elements have been generally used as solid-state image pickup elements that are mounted in electronic endoscopes, in recent years CMOS (a complementary metal oxide semiconductor) type solid-state image pickup elements which enable low-voltage driving and with which demands for larger numbers of pixels and high-speed reading are easily met are also being used.
Further, in the case of utilizing a CMOS type solid-state image pickup element, a CMOS process can be used in the manufacturing process, and peripheral circuits such as a drive circuit or a processing circuit can be combined within the same chip, which is also useful for miniaturization.
For the aforementioned reasons, various kinds of electronic endoscopes equipped with a CMOS type solid-state image pickup element have been proposed in recent years (for example, see Japanese Patent Application Laid-Open No. 2012-143319, Japanese Patent Application Laid-Open No. 2011-206336, and Japanese Patent Application Laid-Open No. 2009-201540).
Generally, in most CMOS type solid-state image pickup elements a plurality of pixels are disposed in a matrix shape on a light receiving surface (image pickup surface), and exposure control by a rolling shutter method is performed. The rolling shutter method is a method that performs an exposure operation for each scan line in a sequential manner, in which resetting is performed in sequence for each scan line and storing of charges is started, and read out of the stored charges is then performed sequentially.